An M5 with a massive boot - sounds win-win to me.

It is, almost. The anomalous M5 Touring is M-division chalk to the M6 convertible's cheese. Both have the same 500bhp V10, yet that the M5 looks absolutely stunning and completely purposeful only serves to emphasise the M6's excesses. But the touring is not perfect, suffering from exactly the same technical frustrations as its saloon namesake, namely the mind-boggling array of set-up choices available.

But isn't choice a good thing?

Yes, but you can have too much of a good thing: three damper settings; traction control that switches between on, off and not-quite-off M mode; three seat settings which squeeze you into the chair ever more aggressively; and a power button to sharpen throttle response and unleash all 500bhp.

Hold on, so you have to tell it to use all its power?

Correct. Otherwise the M5 makes do with a mere 400bhp, so make sure you don't forget to hit the power button if you're going uphill and the boot's full. Talking of which, it would take a shopping spree of Paris Hilton proportions to get anywhere near filling the boot, which at 1650 litres is almost big enough for a grand piano (though you may have trouble playing it). But I wasn't quite finished on the options - the seven speed SMG gearbox has no less than five modes, ranging from soft shifts at low rpms to aggressive jolts at maximum attack in both semi-manual and full automatic. You can, however, save all your preferred settings through iDrive and activate them through the M button on the steering wheel. There's still no manual available in the UK though, and there probably never will be after the US-only M5 stick shifter turned out to be a proper pig's ear. BMW only released it to appease the yanks, too, which goes to show that the customer isn't always right.

So how much will all this space and power cost me?

Let's not mess around, parsimonious it ain't, and coupled with the seventy grand plus you'll pay once you've specced it up a bit, running costs as gargantuan as its luggage area will lighten your wallet, for sure. But things could be worse, given the Touring's genuine dual-identity as performance car and load lugger. Take the supercharged Range Rover Sport, which is nowhere near as practical and even further away from a trackday toy, but which returns less at the pumps than the Touring and churns out more CO2 emissions. Still, at 18.8mpg and 361g/km, the M5 Touring's stats betray its massive ground covering capabilities.

Ok, so let's talk performance then. What's it like to drive?

Once you've got your settings in order, the M5 Touring is as composed and quite frankly superb as the saloon; a true superlative generator. But only in the right situations. Going back to that SMG 'box, with all its available options it plays a massive part in the feel and character of the car dependent on what you're doing. Through heavy traffic, for example, it's best to use a softer setting to make progress smooth and fuss-free. However, find a gap in the traffic, floor it, and you'll find yourself waiting for what seems like an eternity before the 'box composes itself and gets you going again. Technically that would be your fault for being in the wrong mode, but it's an easy mistake to make. And that's a problem, because where a Merc V8 would be alweays raring to go, the M5 is too docile at times and just doesn't feel special enough in moderately heavy traffic. Still, a 0-62mph time of 4.8 seconds and a top speed limited to 155mph tell you it ain't no slouch.

So it's frustrating, but what about on my favourite back road? Surely it's the business there?

You're right. The M5 Touring feels instantly at home on a twisty back road, feeling seriously quick, if hellishly thirsty. From its clattery idle the engine comes alive with induction snorts, soaring revs and aggressively blipped downchanges. Peak power comes in at 8250rpm and its 384lb ft peak torque at 6100rpm, which gives you a positive indication of the Touring's revvy character. Push hard and the M5 gently and predictably understeers, although a couple of downshifts through the sequential 'box and a heavy right foot will get the tail out in a remarkably predictable manner for such a big car. It's best to use the stick through sharp corners because the paddles turn with the wheel. The steering feels meaty and linear, and even in the wet, front end grip is staggering. In its softest setting the ride is still noticeably stiff, but the hardest setting is probably too crashy for most roads.

Verdict

We've always been big fans of the M5 saloon and the extra boot capacity only adds to its appeal. Perfect it's not - the horrendous 15mpg thirst could bankrupt you and the SMG box's jerkiness at parking speeds can be a pain - but if you like your load luggers to have a mean streak, the M5 Touring fits the bill.